Detector



Oct. 11, 1960 H. E. BESTE' 2,956,203

DETECTOR Filed Aug. 51, 1959 lo 40 f DELAY cIRcuIT V V 26 SYNCHRONIZINGHIGH-PASS l4 AMPLIFIER DEFLECTION 2e CIRCUITRY PHASE AMPLIFIER SPLITTERAMPLIFIER NEGATIVE OUTPUT AMPLIFIER L POSITIVE OUTPUT F as J TIMING Fig,CIRCUIT l8 22 20 20 Fig. 2 24 36 F lg. 4

INVENTOR.

HAROLD E. BESTE ATTOR/(IEYS DETECTOR Harold E. Beste, Verona, N.J.,assignor to Allen B. Du Mont Laboratories, Inc., Clifton, NJ., acorporation of Delaware Filed Aug. '31, 1959, Ser. No. 836,966 t' 11Claims. c1. 315-40 This invention relates to a detector, and moreparticularly to one for detecting small objects.

Many types of target detectors are known, someof them, such as radar,producing spots of light, often on a grey or black background. Undersome conditions, this is the only type of display possible, but itrequires interpretation by the user. I Y

A much better type of target detector is one that shows an overalldisplay, containing the target in one part thereof. For example, atelevision-type detector, scanning the sky, would include in itsdisplay: the horizon, clouds, and a small target spot representing anairplane, a missile, etc. This type of display requires nointerpretation,

since the eye readily recognizes the background and the target inrelation thereto. The target spot is usually dark, like a silhouette,but it could be light, if the target happened to reflect the sunlight.The target spot. would always, however, be in some contrast to itsbackground.

For convenience only, the following discussion 'will be presented interms of a dark target spot.-

Detectors of the above television type have one'unfortunate limitation;namely, thefact that in the display the target is a tiny dot, and maynot be readily seen.

It is therefore the principal object of my invention to provide animproved detector. 1

The attainment of this object and others will be realized from thefollowing specification, taken in conjunction with the drawings, inwhich,

Fig. 1 is a block diagram of my invention; and 7 Figs. 2-4 areassociated waveforms.

Broadly speaking, my invention contemplates circuitry that produces adisplay wherein the background is completely shown, and the includedtarget dot "flickers. The flickering target dot attracts attention muchmore readily than if it were merely a spot having fixed contrastrelative to the background. a

The following information will aid in understanding my invention. When atelevision camera scans -a scene, the amplitude of the output signal iscontrolled'by the amount of light reflected by the scene into thecamera. Thus, when the camera scans across a blue sky, the output signalremains at a substantially constant amplitude. When the camera scansacross a cloud, the light reflected into the camera varies from oneportion of the cloud to another. While portions of the clouds range fromWhite to dark grey when viewed by the naked eye, in a close-up viewtaken through a telescope or a television camera, the changes inbrightness are rather gradual. Since the variations in brightness aregradual, they cause the television camera to produce a low frequencyelectrical out put signal.

When the scanning television camera comes to the target, which lookslike a spot against the background, the spot produces a sudden change inthe amount of reflected light and the output signal changes abruptlyfrom one magnitude to another. When the camera leaves the target, theamplitude of the output signal changes suddenly in the opposite sense.These sudden changes cause "ice the television camera to producehigh-frequency electrical output signals.

My invention may -be readily understood by referring to Fig. 1. Since myinvention uses standard television pick-up and display techniques, thesewill not be discussed; theexplanation .being directed only to. thatportion of the television system that embodies my invention. In Fig. 1,the received television signal appliedto terminal 10 is passed throughwell knowncircuits 12 for amplify ing the signals, and through othercircuits, 14 for synchronizing and deflecting the electron beam. Thesecir+ cuits coact to produce on the faceplate of. cathode ray tube 16, adisplay wherein a small dark spot appears against a background of skyand clouds.

In Fig. 2, waveform 18 shows the. output signal from the televisioncamera for .the interval that it is scanning across the portion of thesky containing. the target. The level portions, 20 are of a constantamplitude, representing the output signal produced by the blue sky. Theun dulating portion 22 represents the light reflected by var-' iousportions of the clouds, the higher amplitudes corresponding to the whitecloud portions.- .The negativegoing pulse 24. depicts the reducedreflected light from the target. (If the target were bright, pulse' 24vwould extend upwards.) When waveform 18 is applied to the cathode, raytube, it produces. a linethat (1) is relatively dark at the ends torepresent the blue sky, (2) varies in brightness at the center portionin accordance with the cloud pattern, and (3) contains a dark,-orbright, spot that corresponds to the position of the target.

Referring back to Fig. 1, my invention directs the received televisionsignal through a second path that emphasizesj and operates upon thehigher frequencies that form the dark dot. This circuitry comprisesa'high-pass video amplifier 26,.or, alternatively, separate filters andamplifiers. Circuitry 26 transmits only the high frequency signalcomponents that form the target dot. The output from circuit 26 is thenpassed through a' phase splitter 28. This unit produces a negative-going(normal polarity) and a positive-going (opposite polarity) pulse, thatare in turn applied to amplifiers 30 and 32 respectively. Their outputsare shown in Figs. 3 and 4 respectively, and contain a negative-goingpulse 34'and a positive-going pulse 36. These pulses are of the samewidth as pulse 24, but have a larger amplitude.

I thenuse these opposite polarity pulsesto cause the target dot toflicker. To do this, timing circuit'38 cyclically energizes amplifiers30 and 32 so that the opposite polarity output phlses thereof arealternately applied through video amplifier 12 to cathode ray-tube 16.Timtion of the black and white spots causes the desired flicker.

The foregoing discussion has assumed a tiny target, and my inventiontherefore produces a flickering spot. If the target is larger, eitheractually or because of optical or electrical magnification, theaforementioned high frequency signal components would occur at thetargets outline. Under these conditions, the targets outline wouldflicker while the brightness, or darkness, of the inner portion wouldremain constant.

Under some conditions, a part of the horizon, or a particular portion ofa cloud may be such as to produce a high frequency that produces aflicker. These spurious results are easily discounted, since a targetwould have a continuous movement unlike a horizon flicker which remainsstationary. On the other hand, the changing cloud formations will soonerase the cloudfflicker.

I prefer that the flickering occur about fifteen-times per second, atwhich rate it is most noticeable by the eye. To accomplish this, timingcircuit 38 applies only the negative-going pulse 34 during the first $4of-a second and then applies only the positive-going pulse 36 during thenext of a second. Thus, it takes or of a second for the dot to gothrough a black and White cycle. The resultant flicker rate is thereforefifteen times per second. The same rate may be achieved in a sequentialframe display, by causing each pulseto be produced. during alternateframes, each of which has a duration of of" a second.

A flicker rate of thirty times per second can be produced by causingtiming circuit 38 to apply the pulses for ,6 of a second. The thirtycycle per second flicker rate may be readily produced in a televisionsystem that uses an interlaced field display. Timing circuitry 38 isthen used to cause alternate fields, each of which is of a second long,to produce a dark spot, while the in-between fields produce a lightspot.

If desired for reasons of economy, space, etc., one may eliminate thecircuitry that provides a pulse of the same polarity as the target dot.Under these conditions, at one time the target dot would be normal,while subsequently it would have reversed polarity. The flicker wouldnot be as pronounced, due to the fact that the normal picture would nothave the high frequency emphasisof-the reversed polarity field.

From Fig. 1, it will be seen that the prior art signal path comprisingvideo amplifier 12 will produce the prior art display, wherein a tinydark dot appears against the sky. The operation of my invention is suchthat pulses 24, 34 and 36 coincide, positionwise, with the dark spotthat represents the target. If any appreciable delay is introduced by mycircuitry, a corresponding delay is introduced by delay circuit 40 toproduce the desired superposition.

What is claimed is:

I. In a cathode ray tube display containing a target portion, thecombination comprising: means producing a normal polarity signalcorresponding to said target portion; means producing a reversedpolarity signal corresponding to said target portion; and meanscyclically presenting said normal polarity signal and said reversedpolarity signal whereby said target portion flickers.

In a cathode ray tube presentation containing a target having highcontrast with the background and therefore producing a normal signalpolarity having a high-frequency component, the combination comprising:means separating out said high-frequency component; means energized bysaid high-frequency component for producing an opposite polarity signal;and means alternately applying said normal and said opposite polaritysignals to said cathode ray tube.

3. In a. cathode ray tube presentation. c ntaining. a target having highcontrast, with the background and therefore producing a normal polaritysignal having a high-frequency signal component, the combinationcomprising: means separating out said high-frequency component; meansenergized by sa -id high-frequency component, for producing a normalpolarity signal and an opposite polarity signal; rneansalternatelyapplying said normal and, said opposite polarity signals to said.cathode. ray tube,

4. In a cathode ray tube display containing atarget portion, thecombination comprising: means producing a high-frequency normalpolarity: signal. for. said target portion; means amplifying saidnormal. polarity signal; means producing a higli-fi'equency reversedpolarity signal for said target portion; means amplifying said reversedpolarity signal; means cyclically applying to said cathode ray tube,said amplified: normal polarityr'signal and said reversed polarity;signal, whereby, said, target portion isv alternately brightand; dark,thus causing; said target. portion of said; display to flicker. and be.readily seen.

5. In acathode ray ithe isplay containing a target portion, thecombination comprising: means producing a high-frequency normal polaritysignal for said, target p n; means ampl y g s id no mal pol ty a meansproducing. a high frequency reversedpolarity signal for said targetportion; means amplifying said re? versed polarity signal; meanscyclically applying to said cathode ray tub said ampl fied: normal p lary s gnal and said amplified reversed polarity; signal, said last me nscomp ising a timi g. ir uit, wh r y d target por ion is. ern ely rig tand ark, h s causing said targetpor-tion of said display to. flicker and-be readily seen. .I

6. The. combin i n, of cl im 5 wherein saidz timins' circuit produces a1 5 cycle per-second flicker.

7. The combination of claim 5; wherein said. timing i ui p uc s a 30cycle per sec ndflicker.

n a ho e ray ube present tion o aining a target ha ing h gh on r st withhe background n therefore producing high freq uency signal; n he mination comprisin mea s mplify y aid h gh fr qu n y components; m ansenergized by said amplifier, producing signals1;haying opposite poi,-larities; means mplifying ach said; opp s te polarity Signals; andtiming means. cycl cally applying aid10PP0- s e p la ity sig als to sad, catn deray ube.

9- T e combinat on. of claim 8. whereinsaid iming m a s produc s a 1ycle per-s condsfli k r. 1

11.0- The mbin tion ot a rn 8. wherein s tlnormal nd id pp site pol tysigna are applied-in alternate fields. 5

11. The combination of claim 8 wherein said norma and saidoppositepolarity s ignals;are appliednin. alternate frames.

No references cited.

